Method of preparing alkali metal-containing alloys

ABSTRACT

METHOD OF PREPARING CERTAIN ALKALI METAL-CONTAINING ALLOYS, PARTICULARLY CERTAIN LITHIUM-CONTAINING ALLOYS, COMPRISING VIGOROUSLY ADMIXING A DISPERSION OF MOLTEN ALKALI METAL, PARTICULARLY LITHIUM METAL, IN AN INERT LIQUID WITH ONE OR MORE CERTAIN METALS OR METALLOIDS IN FINELY DIVIDED OR POWDER FORM, AT A TEMPERATURE ABOVE THE MELTING POINT OF SAID ALKALI METAL BUT BELOW THE MELTING POINT OF THE DESIRED ALLOY, AND CONTINUING SAID MIXING UNTIL ALLOYING HAS BEEN EFFECTIVELY ACHIEVED.

United States Patent O 3,563,730 METHOD OF PREPARING ALKALI METAL- CONTAINING ALLOYS Richardo O. Bach and Arthur S. Gillespie, .lr., Gastonia, N.C., assignors to Lithium Corporation of America, New York, N.Y., a corporation of Delaware No Drawing. Filed Nov. 5, 1968, Ser. No. 773,663 Int. Cl. C22b 27/00; 'C22c 1/00, 11/02 U.S. Cl. 75135 14 Claims ABSTRACT OF THE DISCLOSURE Method of preparing certain alkali metal-containing alloys, particularly certain lithium-containing alloys, comprising vigorously admixing a dispersion of molten alkali metal, particularly lithium metal, in an inert liquid with one or more certain metals or metalloids in finely divided or powder form, at a temperature above the melting point of said alkali metal but below the melting point of the desired alloy, and continuing said mixing until alloying has been effectively achieved.

Our invention is directed to a novel method of preparing certain lithium-containing alloys, intermetallic compounds and solid solutions with one or more nonalkali metals or metalloids. The method has a number of advantageous features in that it enables such alloys, intermetallic compounds and solid solutions, hereafter, for convenience, generically called alloys, to be prepared in powdered or finely divided form in a simple and straightforward manner and at relatively low temperatures.

In broad terms, our method involves vigorously mixing a dispersion of a molten alkali metal, particularly molten lithium metal, in an inert liquid medium with one or more certain finely divided or powdered non-alkali metals or metalloids which are capable of forming an alloy with said alkali metal, the mixing being carried out at a temperature above the melting point of the alkali metal but below the melting point of said alloy, and the mixing being continued until alloying has been effectively achieved. This may be effected, for instance, by initially forming a dispersion of the molten alkali metal in the inert liquid medium and then adding thereto the said certain solid finely divided or particulate non-alkali metal and/or the metalloid with vigorous agitation. Alternatively, a dispersion in the inert liquid medium may be made of the said certain solid finely divided or particulate non-alkali metal and/or the metalloid, and then the alkali metal may be added, as solid chunks or as sticks or the like, and vigorous agitation being carried out under conditions while the entire mixture is maintained at a temperature above the melting point of the alkali metal but below the melting point of the alloys. Other alternative specific procedures can be utilized Within the guiding principles and teachings disclosed herein.

Numerous non-alkali metals and metalloids can be used to alloy with alkali metals in accordance with the method of our invention. Illustrative of such non-alkali metals and the metalloids are aluminum, calcium, magnesium, barium, strontium, zinc, copper, manganese, tin, antimony, bismuth, cadmium, gold, silver, platinum, vanadium, indium, arsenic, silicon, boron, selenium, zirconium, tellurium and phosphorus. The non-alkali metals and the metalloids are particularly utilized in finely divided or powdered form, advantageously in the form of atomized powders. Good results are generally obtained utilizing particle sizes in the range of about 1 to about 100 microns, especially preferred being particle sizes in the range of about to 40 microns, but particle Sizes of greater and lesser magnitude can be used.

3,563,730 Patented Feb. 16, 1971 While the various alkali metals can be used, notably sodium, potassium and lithium, as well as mixtures thereof, the method is particularly advantageous for the production of lithium-containing alloys and sodium-containing alloys, as well as lithium-sodium-containing alloys with certain non-alkali metals and/or metalloids. The method is applicable not only to the production of binary alloys but, also, to the production of ternary, quaternary and higher alloys as well. It is especially eflicacious for the production of binary alloys, where the alkali metal or a mixture of alkali metals, say sodium and lithium, is considered as one of the metals of the binary system.

The alkali metal content of the alloys is variable and is, of course, fixed by the amount of alkali metal which is capable of alloying with any given amount of a particular non-alkali metal and/or metalloid or any mixture thereof which is capable of forming alloys. In certain alloy systems, for instance, the alkali metal is capable of alloying with a given non-alkali metal or metalloid in varying atomic ratios so that different alloys of the same elements can be produced.

The inert liquid media in which the molten alkali metals are dispersed must, of course, when operatnig at atmospheric pressure, have boiling points appreciably above the temperatures at which the alloying reaction is carried out pursuant to the practice of our invention. In general, inert liquid hydrocarbons have been found to be most satisfactory since they are inert towards the molten alkali metals as well as towards the non-alkali metals and the metalloids used for producing the alloys as well as toward the produced alloys. Typical of suitable inert liquid media are mineral oils whose boiling points are higher than the temperatures at which the alloying is carried out, for instance, Superla White Mineral Oil #10 (Standard Oil Company of Indiana), petrolatum or petroleum jelly, paraffin waxes, tetrahydronaphthalene, and, in general, inert, aliphatic, cycloaliphatic, araliphatic and aromatic compounds, particularly hydrocarbons.

The proportions of alkali metal, e.g. metallic lithium, and inert liquid medium, or the ratios of metallic lithium to inert liquid medium, are quite variable but, in general, the metallic lithium should constitute from about 5 to about 15%, by weight, of the total mixture, that is, the dispersion of the metallic lithium in the inert liquid medium.

The molten alkali metal dispersion in the inert liquids, such as inert liquid hydrocarbons, in which the alkali metal particles are, for instance, in the range of about 1 to 50 microns, may, if desired, be of the stabilized type. Long chain fatty acids or salts of such acids, such as stearic acid or aluminum stearate, can be used as stabilizers and, where employed, are commonly utilized in small proportions, generally in the range of about 0.5 to 4%, a good average being about 1 to 2%, by Weight of the alkali metal present in the dispersion. Other known stabilizers can be employed, as well as polyhydrocarbon resins which are soluble or colloidally dispersible in the inert liquid hydrocarbons, such resins being exemplified by cross-linked polystyrene resins, a typical example of which is that sold commercially under the trade designation DOW QX3487 (The Dow Chemical Com- P The alloying reaction, as pointed out above, is carried out a temperature which is above the melting point of the alkali metal but below the melting point of the alloy which is being prepared. Thus, for example, in the case of the production of lithium-aluminum alloys, the melting point of which may be 660 C. for higher, depending upon the particular gram atom ratio of the lithium to the aluminum, the alloying reaction is desirably carried out at about 250 C. and desirably not in excess of about 300 C. Generally speaking, the alloying reaction temperatures utilized, while in all cases below the melting points of the particular alloys being produced, are most desirably very substantially below said latter melting points, for instance, one hundred or more degrees centigrade below said latter melting points.

Various of the alloys, in the form in which they are initially prepared in accordance with our present invention, are novel and are characterized by valuable prop erties. Thus, for instance, lithium-aluminum alloy finely divided particles or powders, as prepared at temperatures of the order of about 250 C., appear to be solid solutions. Such finely divided particles or powders are nonpyrophoric. When said as prepared lithium-aluminum finely divided particles or powders are heated to more elevated temperatures, generally in the range of about 400 to 600 C., the solid solutions undergo a change which appears to result in their conversion to intermetallic compounds. The said intermetallic compounds become somewhat pyrophoric. Various other alloy finely divided particles, or powders, produced in accordance with our invention, are, in their as prepared condition, solid solutions which, like the lithium-aluminum solid solutions, are transformed into intermetallic compounds with a change in various of the properties thereof.

The alloys made in accordance with our invention have a variety of uses over and above their usual alloy uses. Thus, for instance, the lithium-aluminum alloys can be used for the production of lithium aluminum hydride, and in lithium batteries or electrochemical power units where the aluminum functions as a conductive supportiong structure. The alloys, as prepared, are generally finely divided particles which can be kept or stored in mineral oil or other inert liquids; or they can be separated as dry particulate materials or powders by washing the dispersions with a hydrocarbon, such as pentane or hexane, and filtering in an inert gas, such as argon, atmosphere.

In carrying out the method of our invention, various inert liquids, proportions thereof, alloying reaction temperatures, equipment and other procedures can be used, but the following has been found very satisfactory as a general procedure:

PROCEDURE A (1) A suitable amount of mineral oil, for example 234 g. of dry Markol-52, is weighed and put into a 1500 ml. s.s. resin pot, equipped with 4-neck s.s. head, larg'on inlet and outlet tubes, dial thermometer and Cowles dissolver-stirrer powered by a Haskins VB-2-18, 18,000 r.p.m. flexible drive motor connected to the power source through a Variac.

(2) The desired amount of alkali metal, for example 28 g. lithium, is added and heated to about 200 C. under argon atmosphere.

(3) The mixture is stirred for about 25 minutes with Variac setting on 50 volts.

(4) A corresponding amount of the finely divided nonalkali metal or metalloid, for example 108 g. of dried Reynolds atomized aluminum powder, is added while stirring.

(5) The mixture is stirred vigorously (Variac on 100) for about minutes to intimately mix the two metals.

(6) If a stabilized dispersion is desired, 2 g. of a dispersing agent is added.

(7) The temperature is raised to about 200 to about 250 C. (in the case of LiAl) and the heating and stirring are continued for an additional approximately 4 hours.

(8) The alloy mixture is then cooled and poured into a suitable container.

The following is a somewhat variant procedure which has also been found to be quite satisfactory as a general procedure:

PROCEDURE B (1) The desired amount of mineral oil is Weighed out and placed in a 500 ml. three-necked stainless steel flask equipped with standard tapered joints. Male joints with gas inlet and outlet tubes are inserted into the two outer necks. The center neck is fitted with a Cole-Farmer Stir-O-Vac stirring assembly attached to its high speed motor. Into one side inlet a dial thermometer is inserted and into the other a small metal flag is placed to break up the mass of liquid during the stirring. An argon supply is attached to one side and a bubble tube to the other.

(2) The desired amount of alkali metal is added to the mineral oil, argon How is. started, and the mixture heated to about 200 C.

(3) Stirring is started and the appropriate amount of alloying metal and/or metalloid is added.

(4) The temperature is adjusted (usually increased to about 250 C.) and a dispersing agent is added.

(5) The reaction mixture is heated and stirred several hours, then cooled and poured into a suitable container.

The following examples are illustrative of the practice of the invention but they are not to be construed as in any way limitative since many other alloys can be produced, and the conditions under which the method is carried out are widely variable as will be apparent to those skilled in the art in the light of the guiding principles and teachings provided herein.

EXAMPLE 1LITHIUM-ALUMINUM Utilizing Procedure A described above, 6.94 g. of Li were reacted with 26.97 g. of A1, namely, a gram atom ratio of 1:1. The resulting alloy particles had a color ranging from jet black to blue grey to grey to brown.

Differential thermal analyses showed no free Li as indicated by no Li endotherm at 180 C. or, in some cases, a very small endotherm. Al endotherms may or may not be present at 660 C. This indicates that in some cases the alloy product may be a mixture of LiAl, Li Al and free Al, instead of pure LiAl. In most DTA runs a large, sharp exotherm occurs somewhere between 400 C. and 600 C., the exact temperature of the exotherm being variable. In several cases, both the exotherm and 660 C. endotherm (Al) appeared with no Li peak at all being evident. This strongly suggests that a phase change occurs with the emission of heat. Two possibilities, at least, exist. These include:

A (a) Li2Al+Al QLiAl-AH A (b) LiAl (phase I) LiAl (phase II) AII The alloy product is variable and is dependent on several things such as reaction temperature, reaction addition mode (whether the Al is added to Li or the Li added to Al, particle size, etc.).

EXAMPLE 2LITHIUM-ALUMINUM Utilizing Procedure A described above, 13.88 g. of Li were reacted with 26.97 g. of Al, namely, a gram atom ratio of 2: 1. Tests on the resulting alloy product showed substantially complete alloying, DTA showing no melting endotherms for Li (180 C.) or Al (660 C.).

EXAMPLE 3LITHIUM-ALUMINUM Utilizing Procedure A described above, 20.82 g. of Li were reacted with 26.97 g. of Al, namely, a gram atom ratio of 3:1. A small Li DTA endotherm was observed as was a broad endotherm at approximately 620630 C. This may have been a depressed Al melting point (Al melts at 660 C.). An estimate based on the Li peak indicated that about of the Li had alloyed with the Al.

EXAMPLE 4LITHIUM-INDIUM Utilizing Procedure A described above, 6.94 g. of Li were reacted with 114.76 g. of In, namely, a gram atom ratio of 1:1. DTA indicated both Li and In endotherms, calculations based upon the area of the In peak indicating that about 57% of the 111 had combined with the Li. A

longer reaction time and more vigorous agitation results in more complete combination of the In with the Li.

EXAMPLE SODIUM-SILICON Utilizing Procedure A described above, 23 g. of Na were reacted with 28 g. of Si, namely, a gram atom ratio of 1:1, the reaction being carried out at 200 C. DTA showed only a small Na peak, indicating substantially complete combination of the Na with the Si as NaSi.

EXAMPLE 6LlTHIUM-SILICON Utilizing Procedure A described above, 6.94 g. of Li were reacted with 28 g. of Si, namely, a gram atom ratio of 1:1. DTA indicated that the resulting alloy satisfied the formula LiSi. So far as has been ascertained, LiSi is a heretofore unknown compound.

EXAMPLE 7LITHIUM-MAGNESIUM (a) Utilizing Procedure A described above, four different preparations were made, in each instance the Li and Mg being used in a gram atom ratio of 2:1. In the first of said preparations, the Mg was used in granular rather than powder form. Alloying successfully was achieved. In the second and third preparations, the lithium employed contained, respectively, 0.56% and 0.005% Na, and the Mg utilized was a Gallard-Schlesinger-200+325 mesh Mg powder which was carefully protected from the atmosphere. The fourth preparation was one in which the weight ratio of the Li to the Mg was such that the final alloy contained 13% Li for use in powder metallurgy.

EXAMPLE 8LITHIUM-ZINC Utilizing Procedure A described above, 13.88 g. of Li Were reacted with 196.14 g. of Zn, namely, a gram atom ratio of 2:3. The resulting well defined alloy (intermetallic compound Li Z113) was jet black and separated from the mineral oil, leaving a crystal clear mineral oil layer. DTA on the powder indicated no exotherms for Li or Zn.

In determining, in any given case, whether reaction or alloying has occurred between the alkali metal and the non-alkali metal or metalloid, a physical observation in many cases suffices to show when an unreacted mixture results. In such cases, generally speaking, where lithium is the alkali metal and where the non-alkali metal is, for instance, aluminum, said nonalkali metal sinks in the mineral oil or like inert liquid, while the free lithium metal floats on the surface. This observation can be accelerated by diluting about 10 with hexane. A successful preparation is indicated by failure of the lithium metal to separate.

When alloy formation has occurred, this is also generally readily ascertainable by microscopic examination. The alloy manifests itself, for instance in the case of lithiumaluminum alloys, by its irregular-shaped black particles of about 10 to 50 micron size. Any free lithiurn appears as small spherically-shaped particles of about 1 to 10 micron size.

A more meaningful study of alloy formation involves a differential thermal analysis (DTA) of powders obtained by washing the dispersions With hexane and filtering and drying the powders in an inert gas, e.g., argon atmosphere. The samples are then put into a differential thermal analyzer cell and run against an inert alumina reference sample. The temperature is increased through the 180 C. melting temperature of lithium. Any free lithium is indicated by an endotherm peak at 180 C We claim:

1. A method of preparing an alkali metal-containing alloy in particulate form which comprises vigorously mixing, with molten alkali metal dispersed in an inert liquid medium, at least one member selected from the group consisting of (a) solid metalloids, in particulate form, and (b) solid non-alkali metals, in particulate form, selected from the group consisting of aluminum, calcium, magnesium, barium, strontium, zinc, copper, manganese, tin, bismuth, cadmium, gold, silver, platinum, vanadium, indium, selenium, zirconium and phosphorus, capable of forming an alloy with said alkali 'metal, said mixing being carried out at a temperature above the melting point of said alkali metal but below the melting point of said alloy, and continuing said mixing until alloying has been effectively achieved.

2. The method of claim 1 in which the solid nonalkali metals and solid metalloids are in the form of powders having a particle size in the range of about 1 to 100 microns.

3. The method of claim 2 in which the inert liquid is a mineral oil.

4. The method of claim 3 in which the alkali metal is lithium and the powdered non-alkali metal is aluminum.

5. The method of claim 4 in which the gram atom ratio of the aluminum to the lithium in said alloy is in the range of from 1:1 to 1:3.

6. The method of claim 5 in which the temperature at which alloying is effected is in the range of just above the melting point of lithium metal to about 300 C.

7. The method of claim 1 in which a dispersion stabilizer is incorporated into said dispersion.

8. The method of claim 7 in which the stabilizer is a resin.

9. The method of claim 3 in which the alloy is separated from the mineral oil by washing with an organic solvent and filtering.

10. The method of claim 1 in which the temperature at which the mixing is carried out is at least 100 C. below the melting point of the alloy.

11. The method of claim 1 in which the alkali metal is lithium and the non-alkali metal is magnesium.

12. The method of claim 1 in which the alkali metal is lithium and the non-alkali metal is zinc.

13. The method of claim 1 in which the alkali metal is lithium and the non-alkali metal is indium.

14. The method of claim 6, which includes the steps of decovering the aluminum-lithium particulate alloy from the reaction medium and heating it at an elevated temperature to convert it into an intermetallic compound.

References Cited UNITED STATES PATENTS 1,922,037 8/ 193 3 Hardy 58X 2,085,802 7/1937 Hardy 7558 2,687,951 8/1954 Whaley 7505 2,731,342 1/ 1956 Pfefferkorn 75134 2,849,309 8/1958 Whaley 75135 2,978,304 4/1961 Cox 75134.5X 3,041,164 6/1962 Cox 75134 3,442,923 5/1969 Gray et al 75.5 3,492,114 1/ 1970 Schneider 7553 3,501,291 3/1970 Schneider 75129X L. DEWAYNE RUTLEDGE, Primary Examiner I. E. LEGRU, Assistant Examiner US. Cl. X.R. 75-0.5, 134

Patent No. 3 Dated February 16, 1971 I Ricardo 0. Each and Arthur S. Gillespie, Jr.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

The first name of the inventor, RICARDO 0. EACH, is

misspelled as "RICHARDO", and should be spelled "RICARDO";

and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Pa tent Office.

Signed and sealed this 22nd day of June 1 971 (SEAL) Attest:

EDWARD M.FLE1CHER,JR. WILLIAM E. SCHU'YLER Attesting Officer Commissioner of Pat 

